1. Field of Invention
The invention relates generally to an application technique using holography, and more particularly, to a method of producing a projection holographic screen for displaying a three-dimensional color images.
2. Description of the Related Art
A projection holographic screen is a kind of holographic optical element that serves as a general image display screen where an image, being projected on the screen, can be observed if an eye is disposed within a limited viewing zone. In order to observe a stereoscopic or multiview image, the viewing zones should be narrow enough to deliver to the left and right eyes of the viewer the left and right images correspondingly. For projection of the stereoscopic image the viewing zone centers should be spaced apart from each other by an eye-to-eye distance (about 6.5 cm).
There are two types of the projection holographic screens known in the art, i.e., a reflection type and a transmission type. The holographic screen of the reflection type selectively displays only an image projected through a projector on the screen, while serving as a reflection mirror having a focusing capacity which allows an image of the exit pupil of a projection lens to be focused to form the viewing zone. However, as this type of holographic screen has a high angular and spectral selectivity, only a monochromatic image with a limited viewing zone can be displayed on the screen. Further, three holographic screens of the reflection type formed by red, blue and green lasers should be stacked to display a color image.
The transmission type holographic screen is formed as a hologram of the diffusive light scatterer. When the screen is illuminated by the projected image the light scattered by the screen surface is directed to the predefined domain or viewing zone. The properly produced holographic screen as seen from the viewing zone should have the uniform illumination of all its surface and true color reproduction. These peculiarities depend of the screen recording method.
In the conventional setup for the holographic screen recording as disclosed, for example, in U.S. Pat. No. 4,799,739 and PCT International Publication WO 93/02372, a converging reference wave is made to interfere on a holographic photoplate with an object wave incident upon the photoplate via a diffuser. Being illuminated by the projector, the holographic screen is forming the real image of the diffuser in front of the screen, the viewing zone coincides with this image. The most serious drawback of the described setup is the necessity to use big size optics for the screen recording: at least one lens should be bigger than the screen itself.